Rosemary is not a long lived plant and will get leggy and dead looking if you do not prune it every year. What I would do is prune the rosemary as much as you can within the fresh growth - not in the woody parts - and then root the cuttings. You can even root rosemary in water. Just take a 10-15 cm cutting, remove the lower leaves and put in water. You can also root in sandy soil like Lavender. Use those cuttings to fill in the gaps in your hedge.

To keep the new plants looking good longer, prune frequently and lightly, and prune so that the top is narrower than the bottom--letting it mushroom out is a sure way to get a leggy base.

I agree totally with both Kildermorie and Tugbrethil. I reckon to have to expect to replace my rosemary bushes every five years or so, because they get too big and shapeless - they get leggy very easily. I have about 50 cuttings taken this last year, sitting, waiting to fill in gaps and replace plants that have got too big for their space. I prune my constantly, I suppose, by taking large sprigs throughout the year for cooking!

Cuttings are really easy from Rosemary...luckily! Take lots and you'll have some to give away too. Wait until early summer before taking cuttings from the newest growth or side shoots torn off to leave a 'heel'. Use a sandy compost in pots or trays. Keep them somewhere light but not in direct sunlight. In a cold frame or somewhere else sheltered from drying winds. Even a plastic bag over the pot will do.

If you have lavender, too, Mazzarelli, you'll find the same things apply - they have a limited shelf-life(!) and need to be replaced from time to time.

We have some 15-20 year old rosemaries here in the desert, but they are huge, unpruned specimens. No attempt to keep them small!

I prune the dead flower heads in summer/autumn (weather and flower dependant) and again trim fresh growth down in march. Sounds like you are cutting off new flower buds in the spring but it works to keep plants compact, and they still flower every summer.

Umm...Avkq47? Rosemary has tiny sprays of blossoms mixed with the foliage all along the new growth. What kind of plant are you pruning?

Rosemary and lavender hedges and plants - I lightly shave them with my hedge trimmers in march. They are encouraged to sprout further down the stems and flower beautifully every year. Helps to keep them compact. Rosemary can take a harder shave of the new growth, but like lavender, doesn't like its old wood being cut unless you really need to severely cut down, in which case forego flowers for one year and prune when all danger of frosts have passed. They can still get too large, and many recommend replacing every 5 or so years with new plants. As Gattina says - Mazzarelli's plants sound like they need replacing.